Separating and recovering nonferrous alloys from ferrous materials coated therewith



United States Patent SEPARATING AND RECOVERING NONFERROUS ALLOYS FROM FERROUS MATERIALS COATED THEREWITH Ralph A. Schaefer, Cleveland, and George R. Kingsbnry, 'Gates Mills, Ohio, assignors to 'Clevite Corporation,

Cleveland, Ohio, a corporation of Ohio No "Drawing. Application November '22, 1954, Serial No. 470,537

Claims. (Cl. 204-446) This invention relates to processes for separating and recovering a nonferrous alloy from a ferrous material coated therewith, and more particularly to a process of separating and recovering a nonfcrrous lead-bearing copper base alloy affixed to a ferrous material such as steel.

Copper base alloys and steel are found affixed together as unitary bodies in composite stock, which is available, for example, in the form of scrap comprising a steel material to which the copper base alloy adheres as a result of a casting, sintering, or electroplating operation. The removal and recovery from steel or brasses or bronzes, such as gilding metal, have been investigated prior to the present invention. Thus it has been proposed to employ an electrolytic operation, using an electrolyte containing sodium cyanide, often with inclusion of trisodium phosphate, to remove copper-zinc alloys from steel and obtain a cathodic deposit of dense, homogeneous gilding metal in the same operation. However, attempts to adapt such processes to the separation and recovery of lead-bearing copper base alloys affixed to steel hitherto have proved unsuccessful.

Proposals also have been made for obtaining smooth, uniform electrolytic deposits of silver, copper, lead, and alloys such as silver-lead and copper-lead alloys. In the case of these binary alloys one such proposal involves the use of anodes which provide separate controlled surface areas of the two metals, and which are small enough so that the anode current density is of the order of 30 to 50 amperes per square foot while the cathode current den sity is less than half of the anode current density. This same proposal also suggests addition of so-called corrosive ions, such as tartrate and citrate ions, to the cyanide plating bath in large quantities, for example by the inclusion in the electrolyte of 5t) grams per liter of potassium tartrate. However, such a plating operation utilizes a carefully prepared, completely nonferrous anode of unalloyed metals, and so does not operate to remove an alloy of nonferrous metals from a composite body including a ferrous component. Furthermore, these methods of the prior art provide an electrodeposited alloy which is not separately recoverable from the cathode structure used because of the hard, dense, and strongly adherent nature of the cathodic deposit.

Accordingly, it is an object of the present invention to provide a new and improved process of separating and recovering a nonferrous alloy from a ferrous material coated therewith which substantially eliminates some or all of the disadvantages of the prior art processes.

It is another object of this invention to provide a new and improved process of separating and recovering a nouferrous alloy from a body thereof including a ferrous material with substantially complete separation and recovery of the ferrous and nonfcrrous constituents of the body.

It is a further object of the invention to provide a process of both separating and recovering a nonferrous alloy from a ferrous material coated therewith which involves the use of an electrolyte composition providing high etficiency and economy of such separation and recovery.

It is yet another object of the invention to provide a new and improved process of electrolytically separating and recovering a nonferrous lead-bearing copper alloy coated on a ferrous material without undesirable oxidation reactions taking place on any anodic surface.

It is a still further object of the invention to provide a process of separatingand recovering a nonferrous alloy from a ferrous material coated therewith in which the alloy is recovered in the form of a spongy deposit that can be easily segregated and pulverized to produce a powder suitable for use in fabricating articles by thetechniques of powder metallurgy.

In accordance with the invention, the process of separating and recovering a nonferrous alloy from a ferrous material coatedtherewith comprises placing a body made up of a nonferrous lead-bearing copper base alloy affixed to a ferrous material in a strongly alkaline aqueous electrolytecontaining an alkali metal cyanide and between 5 and 20 grams per liter of the tartrate radical Electric current is passed between this body as an anode and a cathode structure, the anode-cathode potential being maintained at a value producing a potential drop of less than about 0.8 volt between the anodic body and the portions of the electrolyte in the vicinity thereof, whereby the copper base alloy, including the lead, is anodic-ally dissolved, without substantial attack on the ferrous material of the body or destruction of the cyanide or tartrate in the electrolyte, to effect its separation from the ferrous material, the copper base alloy being substantially recovered in metallic form on the cathode structure.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description, and its scope will be pointed out in the appended claims.

The process, described hereinbelo-w, of separating and recovering a nonferrous alloy from a ferrous material coated therewith comprisesplacing one or more bodies, each made up of a particular nonferrous lead-bearing copper base alloy affixed to a ferrous material, in an electro lytic bath which is suitable for use not only in separating all constituents of the nonf-errous alloy from the ferrous material to which the alloy is afiixed but also in effecting cathodic deposition of the constituents of the nonferrous alloy on a cathode structure. In the usual case, the lead-bearing copper base alloy to be separated and recovered contains at least 55% copper and between 1% and 40% lead. Separation and recovery of such a leadbearing copper base alloy also can be effected in accordance with the invention when the alloy contains up to about 15% tin, up to about 10% zinc, and up to about 10% nickel. Up to about 2% each of one or more additional nonferrous metals may be included in the alloy without adversely affecting the separation and recovery. Of course, suitable adjustments must be permitted in the composition of the electrolyte before adequate recovery of adidtional constituents of the lead-bearing copper alloy can be expected. Thus a typical coating which may be removed from a steel backing structure and recovered by the process of the present invention contains about copper With or Without, say, about 3.5% tin and 1.5% zinc, the balance being lead.

Nonferrous alloys of the type just described find use in the fabrication of bearing surfaces on steel backing structures. Another example is a well known alloy including 10% lead and 10% tin, the balance being copper. Further examples of such copper base alloys are a bushing alloy containing 8% lead, 4% tin, 3% zinc, and the balance copper, and a nickel Phosphor bronze contain- 3 ing 11% tin, 1.5% lead, 1% nickel, and the balance mostly copper. It will be apparent to those skilled in the art, from the discussion hereinbelow, that lead-bearing copper base alloys having a wide range of compositions may be separated from the steel and substantially recovered in accordance with the present invention.

The body made up of the nonferrous alloy aflixed to the ferrous material is placed in a strongly alkaline aqueous electrolyte containing an alkali metal cyanide and between 5 and 20 grams per liter of the tartrate radical -OOC-CHOHCHOHCOO. In discussing the composition of the electrolyte hereinbelow, reference will be had to ions of the metallic constituents of the electrolyte, since in general the salts and hydroxides of these metals are very highly ionized in the electrolyte. For present purposes it will be assumed that complex ions, in which some of the metal ions may be bound, are equivalent to the completely dissociated simple ions of these metals. Accordingly it can be considered for purposes of describing the composition of the electrolyte that all of the copper present, for example, is present in the form of copper ions. However, to avoid any questions regarding the extent of ionization of tartrates present in the bath, reference will be made only to the dibasic tartrate radical itself. In any electrolyte used for carrying out the present invention this radical will be effective without any determination of the extent of dissociation of the salt or acid compound structures in which each of the two carboxyl groups of the tartrate might be combined. Thus an alkali metal tartrate such as potassium tartrate, or sodium tartrate, or Rochelle salt may be dissolved in the bath and will be ionized to any extent necessary to aid in the anodic solution and cathodic recovery of the nonferrous alloy constituents. Rochelle salt, for example, may be used in quantities between approximate limits of somewhat less than grams per liter and somewhat more than 38 grams per liter. Use of tartrate in amounts substantially in excess of those specified hereinabove not only is uneconomical in formulating the electrolyte for a process of the type under discussion, but materially increases the tendency toward destruction and loss of tartrate through oxidation during operation of the electrolytic cell. While the tartrate radical is necessary to effect removal of lead from the scrap alloy and to stabilize the lead ions in solution, it is an advantage of the process of the invention that concentrations of the tartrate radical greater than grams per liter are unnecessary, so that the expense of adding. maintaining, and controlling higher concentrations is avoided. Various hydroxy acid compounds other than the tartrates also have been tried, but experience indicates that the maintenance of an active surface which permits continued eflicient anodic solution of the copper-lead alloy requires the presence of the tartrate radical.

It is preferred that the aqueous electrolyte have a composition falling within the limits given in Table A:

Table A Copper ions g./l 10-50 Lead ions g./l 0.5- 5 Other nonferrous alloy metal ions g./l 0.0-15 Alkali metal hydroxide g./l 5-50 Free alkali metal cyanide g./l 2.5-15 Alkali metal carbonate Substantial Tartrate radical It is noted that the concentration of the alkali metal hydroxide may be controlled with rather Wide limits. Electrolytes of the compositions covered in Table A are strongly alkaline. The concentration of free alkali metal cyanide also may be maintained within rather wide limits. The free cyanide may be defined in a conventional manner as essentially that in excess of the amount required to form the corresponding alkali metal cuprocyanide with the copper present in the solution. It can be determined by the standard Volhard titration. The free cyanide content ordinarily is held above about 5 grams per liter, while the alkali metal hydroxide ordinarily is held above about 20 grams per liter. Between 20 and 30 grams per liter of Rochelle salt is recommended.

The alkali metal carbonate may be present in the bath in rather small quantities or up to its saturation value at the temperature involved. Substantial quantities are practically unavoidable, since some atmospheric oxidation of cyanide to produce carbonate is almost inevitable over extended periods of time.

It will be understood that the concentrations of copper and lead ions and of the ions of any other nonferrous alloy metals present will approach individual equilibrium values if the same nonferrous alloy is to be dissolved in and recovered from the same bath over extended periods of time. The composition of the bath tends to adjust itself so that the metals are deposited at the cathode in the same proportions as they are present in the nonferrous alloy being separated and recovered. This ad-.

justment may be hastened by arranging the composition of the bath to approximate the equilibrium concentration for the alloy involved.

The following examples will illustrate the choice of electrolyte compositions. It will be understood that corresponding potassium compounds, for example, may be substituted for the sodium compounds mentioned. If metals other than copper and lead are present in the hearing metal or other alloy to be recovered, it is advantageous to introduce them in the electrolyte in soluble form by adding a corresponding soluble alkali metal compound of each such metal.

The approximate bath composition given in Table B was found to be effective in recovering a bearing metal composed essentially of 77% copper and 23% lead:

Table B Gm./l. Copper 20 Lead 1 Sodium hydroxide 35 Free sodium cyanide 10 Sodium carbonate 40 Rochelle salt 20 Scrap bodies made up of bearing metal coated on steel in mixed sizes and shapes were placed in perforated steel baskets as anodes in a steel tank containing a bath of this composition. A cathode of sheet steel was placed in the bath. A variety of cathode structures, for example of steel or copper, may be used. Bath temperature was maintained at about 80 C.

Electric current then was passed between the scrap bodies as anode and the steel cathode structure. The anode-cathode potential was carefully controlled so as to maintain it at a value producing a potential drop of less than about 0.8 volt between the anodic scrap bodies and the portions of the electrolyte in the vicinity thereof.

The total voltage across the cell from anode to cathode required to pass a given amount of current and to obtain the desired potential drops will vary with the type of equipment used, the distance between electrodes, and the conductivity of the bath. The total voltage therefore is not a satisfactory value for defining or controlling the process. The actual anode potential is the critical factor. It can be determined by inserting a probe electrode of a metal chemically inert to the bath, such as a steel elec trodc, into the bath in the vicinity of one of the anodic bodies and measuring the potential between the probe electrode and the anode with a high resistance voltmeter. The distance between the anode and the probe electrode is not important when a meter having a resistance of, say, 20,000 ohms per volt, is used, so long as the probe does not touch the anode film. After adjustment of the cell voltage to obtain the proper anode potential drop, the total voltage between anode and cathode can be adopted as an operating guide and maintained as long as the variables other than anode potential which combine to atfect the cell voltage remain constant.

The voltages between the anode and the adjacent electrolyte may fall as low as 0.7 volt or lower. However, the lower voltages ordinarily are less desirable, since the stripping rate diminishes roughly in proportion to the decrease in this voltage.

In any case, as a result of the arrangement of the electrolytic cell and the maintenance of the cell voltages described hereinabove, the copper base alloy, including the lead, is anodically dissolved. This anodic solution is selective and takes place, without substantial attack on the ferrous material or destruction by anodic action of the cyanide or tartrate in the bath, to effect separation of the nonferrous alloy from the ferrous material, and the alloy is substantially recovered in metallic form on the sheet cathode structure.

In the example given, the metallic deposit on the cathode was in the form of a sponge, averaging in composition about 23% lead and the balance copper. The cathode current efficiency was found to be about 95 and the anode current efficiency about 98%, calculated on the basis of bearing metal dissolved.

Bearing metal scrap of other compositions, as mentioned hereinabove, may be treated in accordance with the invention. In the manufacture of certain types of bearings, a molten mixture of bearing metal having the approximate composition of 72% copper, 23% lead, 3% tin, and 2% zinc, is cast onto a steel backing material such as a continuous strip or a formed shell. This strip or casting is subjected to further operations such as trimming, stamping, and shaving, with the result that a consider able amount of composite scrap, consisting of steel and adherent bearing metal, accumulates. This scrap likewise may be charged into perforated steel baskets and immersed in an electrolyte of selected composition. The baskets are made anodic in an electrical circuit with a suitable cathode. In an example using the scrap just described, the electrolyte was compounded to have the approximate composition given in Table C:

Table C Gm./l. Copper 20 Lead l Tin 5 Zinc 1.5 Sodium hydroxide 35 Free sodium cyanide l0 Rochelle salt 30 Sodium carbonate 40 Again the required electrical potentials were maintained in the anode-cathode circuit with the bath at an operating temperature of about 80 C., and a nonferrous material was deposited at the cathode.

The exact composition of the alloy thus recovered initially may deviate somewhat from that of the nonferrous alloy in the scrap bodies, but a little care in compounding the electrolytic bath will insure that the alloy recovered has a composition similar to that of the starting alloy. Thus the metal recovered in the example given hereinabove, after washing and drying, analyzed within the following limits with individual variations from batch to batch: lead, l8-25%; tin, l-4%; zinc, 0.53%; and the balance copper. Over a period of time, of course, the analysis of the alloy recovered tends to approach the composition of the starting scrap, and this is accomplished without excessive build-up of any metal ion in the electrolyte. In practice, bath compositions and cathodic deposit analyses vary with the exact composition of the nonferrous metal content of the scrap used as anodes.

Accordingly, the relative concentrations of the metals initially in the electrolyte are not very important, since they tend to adjust themselves to equilibrium values which provide a cathode deposit approximating the analysis of the copper base alloy anode composition. The metal ion concentrations cited in the examples given hereinabove have been determined experimentally, and equilibrium operating conditions for the scrap compositions involved can be established rapidly if the metals present in the nonferrous material to be recovered are originally included in the bath in the approximate ratios indicated in these examples. Lead can be added as oxide or basic carbonate, tin as sodium stannate, and zinc as the oxide or carbonate. Of course, any compound of these metals soluble in the alkaline bath can be used, but it is preferable to keep extraneous anions, such as chloride, sulfate, or nitrate, out of the bath; their absence simplifies analysis and control.

In charging the scrap to be treated, a series of baskets containing the steel and bearing metal mixtures preferably is placed in the tank, one at a time, at regular intervals. When all the bearing metal in one basket has been dissolved, leaving only bare steel, that basket is replaced. The series of baskets may be given a slow oscillatory motion to tumble the anode pieces. Thus there is available to the electrolyte at all times a succession of composite scrap bodies containing steel and bearing metal in various proportions. This assures a reasonably constant bearing metal surface area while providing for practically complete dissolution of bearing metal from the bodies in each individual basket. This makes it possible to main tain a steady current without exceeding the critical anode potential discussed hereinbelow.

The most important factor in minimizing anodic destruction or oxidation of bath constituents and assuring efficient dissolution of bearing metal is maintenance of the potential between the anodic members and the neighboring electrolyte below the aforementioned maximum value of about 0.8 volt. Excellent results have been obtained by maintaining this potential at essentially 0.70 volt. Potentials of much over 0.8 volt bring about extensive and uneconomical destruction of cyanide and tartrate through oxidation at the steel surfaces. With the recommended potential drops, passage of the electrolytic current effects separation of the copper base alloy from the ferrous material without undesirable anodic oxidation of other materials.

During electrolysis it has been found advantageous to circulate the solution by means of a pump and to filter it continuously. It also is highly advantageous to maintain relative agitation of the cathode structure and the electrolyte. This may be effected by imparting motion to the cathode structure as well as to the anode baskets during electrolysis. By circulating the solution. filtering it continuously, and moving the cathode and anode the composition of the electrolyte and the composition and physical condition of the cathodic deposit are stabilized and optimum conditions for most efiicient operations are obtained.

To obtain on the cathode a spongy deposit which can be processed easily into a dry metal powder of desirable physical properties for use in powder metallurgy, the size of the cathode structure should be adjusted for a cathode current density of between about 30 and amperes per square foot or more with cathode agitation of about 5 linear feet per minute or more produces excellent results. Without such cathode motion or some other relative agitation of the cathode and the electrolyte, a cathode current density of 20 amperes per square foot probably represents an average current for practical operation. With gentle relative cathode-electrolyte agitation, that is, from several feet per minute up to about 10 feet per minute, the optimum current density is in the above-mentioned range of about 30-80 amperes per square foot, while high rates of agitation, in the neighborhood of 20 feet per minute, would permit cathode current densities as high as about 100 amperes per square foot.

When the gentle relative agitation is maintained with cathode current densities of about 30-80 amperes per square foot, it is particularly easy to recover the copper base alloy in metallic form as a spongy deposit on the cathode structure. This spongy deposit, accumulated on the cathode, can be removed readily by scraping from the cathode structure at convenient intervals to segregate an easily powderab-le alloy having a composition similar to that of the lead-bearing copper base alloy on the bodies charged into the tank. The segregated material may be washed in water until it is practically free from electrolyte, air-dried at temperatures under about 120 C. to minimize oxidation, and ball-milled or otherwise treated with a minimum expenditure of time and energy to reduce the accumulated lumps to a fine, uniformly sized powder. The powder may be stored in essentially air-tight containers to avoid atmospheric oxidation.

It is noted that the scrap material ordinarily used in the process of the invention has little value until separated into its two principal components, steel and bear ing metal alloy. The values can be recovered by the process of the invention, however, since the resulting steel may be utilized as high grade scrap and the bearing metal may be used again as such. Separation by thermal or mechanical means results in high economic losses, and the process of the present invention is the first which has been found to eliminate such high losses. The cathodic deposit in the form of a spongy powder can be recovered, washed, dried, broken up, and mixed to produce a bearing metal powder suitable for forming bearings by the conventional processes of powder metallurgy, and the powder so produced is as useful as, and much cheaper than, a similar powder made by conventional processes involving comminuting the alloy constituents separately and then mixing them, or reducing massive alloy to powder form. The steel needs only to be rinsed and dried for utilization as top grade clean scrap. Of course, if the cathode conditions are not adjusted as recommended hereinabove, a dense deposit, for example on a non-ferrous cathode suitable for remelting, can be obtained.

While there have been described what at present are considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, to cover in the appended claims all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The process of separating and recovering a nonferrous alloy from a ferrous material coated therewith, comprising: placing a body made up of a nonferrous lead-bearing copper base alloy aflixed to a ferrous material in a strongly alkaline aqueous electrolyte containing an alkali metal cyanide and between 5 and 20 grams per liter of the tartrate radical rous material or destruction of said cyanide or tartrate,

to effect separation from said ferrous material, and is substantially recovered in metallic form on said cathode structure.

2. The process of separating and recovering a nonferrous alloy from a ferrous material coated therewith,

comprising: placing a body made up of a nonferrous alloy, containing at least 55% copper and between 1% and 40% lead, affixed to a ferrous material in a strongly alkaline aqueous electrolyte containing an alkali metal cyanide and between 5 and 20 grams per liter of the tartrate radical -OOCCHOHCHOH--COO; and passing electric current between said body as anode and a cathode structure, the anode-cathode potential being maintained at a value producing a potential drop of less than about 0.8 volt between said anodic body and the portions of the electrolyte in the vicinity thereof, whereby said nonferrous alloy, including said lead, is anodically dissolved, without substantial attack on said ferrous material or destruction of said cyanide or tartrate, to effect separation from said ferrous material, and an alloy having a composition similar to that of said nonferrous alloy is recovered on said cathode structure.

3. The process of separating and recovering a nonferrous alloy from a ferrous material coated therewith, comprising: placing a body made up of a nonferrous lead-bearing copper base alloy affixed to a ferrous material in an aqueous electrolyte of the following composition:

Copper ions g./l 50 Lead ions g./l 0.5- 5 Other nonferrous alloy metal ions g./l 0.0 Alkali metal hydroxide g./l 5-50 Free alkali metal cyanide g./l 2.5-15 Alkali metal carbonate Substantial Tartrate r a d i c a l OOC-CHOHCHOH COO- g./l 5-20 and passing electric current between said body as anode and a cathode structure, the anode-cathode potential being maintained at a value producing a potential drop of less than about 0.8 volt between said anodic body and the portions of the electrolyte in the vicinity thereof, whereby said copper base alloy, including said lead and any other nonferrous metals therein, is anodically dissolved, without substantial attack on said ferrous material or destruction of said cyanide or tartrate, to effect separation fr-om said ferrous material, and is substantially recovered in metallic form on said cathode structure.

4. The process of separating and recovering a nonferrous alloy from a ferrous material coated therewith, comprising: placing a body made up of a nonferrous leadbearing copper base alloy affixed to a ferrous material in a strongly alkaline aqueous electrolyte containing an alkali metal cyanide and between 5 and grams per liter of the tartrate radical OOCCHOH----CHOH- COO-, and passing electric current between said body as anode and a cathode structure, the anode-cathode potential being maintained at a value producing a potential drop of approximately 0.7 volt between said anodic body and the portions of the electrolyte in the vicinity thereof, whereby said copper base alloy, including said lead, is anodically dissolved, Without substantial attack on said ferrous material or destruction of said cyanide or tartrate, to effect separation from said ferrous material, and is substantially recovered in metallic form on said cathode structure.

5. The process of separating and recovering a nonferrous alloy from a ferrous material coated therewith, comprising: placing a body made up of a nonferrous leadbearing copper base alloy aflixed to a ferrous material in a strongly alkaline aqueous electrolyte containing an alkali metal cyanide and between S and 20 grams per liter of the tartrate radical OOC- CHOHCHOH-COO--, passing electric current between said body as anode and a cathode structure, the anode-cathode potential being maintained at a value producing a potential drop of less than about 0.8 volt between said anodic body and the portions of the electrolyte in the vicinity thereof, to effect separation of said copper base alloy, including said lead, from said ferrous material by selective anodic solution without substantial attack on said ferrous material or destruction of said cyanide or tartrate', maintaining gentle relative agitation of said cathode structure and said electrolyte, the size of said cathode structure being adjusted for a cathode current density of between about 30 and 80 amperes per square foot, substantially to recover said copper base alloy in metallic form as a spongy deposit on said cathode structure; and scraping said spongy deposit from said cathode structure to segregate an easily powderable alloy having a composition similar to that of said lead-bearing copper base alloy.

References Cited in the file of this patent UNITED STATES PATENTS 1,867,527 Dunn July 12, 1932 10 2,198,365 Cinamon Apr. 23, 1940 2,545,566 Booe Mar. 10, I951 FOREIGN PATENTS 525,364 Great Britain Oct. 27, 1939 OTHER REFERENCES o and 678 pertinent.

The Monthly Review" (American Electroplaters Society), November 1943, page 1007. 

3. THE PROCESS FO SEPARATING AND RECOVERING A NONFERROUS ALLOY FROM A FERROUS MATERIAL COATED THEREWITH, COMPRISING: PLACING A BODY MADE UP OF A NONFERROUS LEAD-BEARING COPPER BASE ALLOY AFFIXED TO A FERROUS MATERIAL IN AN AQUEOUS ALECTROLYTE OF THE FOLLOWING COMPOSITION: 